The advancement of the state of the art of fiber laser technology has been quite rapid over the past decade. The increasing availability of efficient, powerful pump laser diodes and the development of pump combiner devices and attendant optical matching components has pushed attainable output power and radiance to previously unseen levels. However, the tools for constructing such devices have not kept pace. Assembly of high-power fiber lasers and their components has remained a skilled craft, requiring lengthy manual processes and delivering low production yields.
Due to the high optical power levels involved, and especially with the development of cladding-pumped designs, the requirements for alignment, cleave quality, cleanliness, and correct splice, taper, and diffusion geometry are more stringent than even the most critical of previous lower-power applications. Cleave angle specifications for 125 μm telecom splices typically allow 1° or more of deviation from the perpendicular, compared to a high power splice which might require <0.25° on fibers which are more challenging to cleave. Optical losses of 0.1 dB, which might be acceptable for a splice in a telecom erbium-doped fiber amplifier (EDFA), will dissipate over 20 W in a kilowatt laser, causing explosive failure of the splice. As well as splicing, the assembly process may require various tapering procedures to create combiners and mode field adapted splices. These tapers must have correct adiabatic core geometry and in some cases a surface free of contaminants, which can cause destructive “hot spots.”
In the 1990's, several manufacturers introduced fiber preparation and fusion splicing machines that enabled the high-volume production of EDFA's for the telecom boom. These machines employed varying degrees of fixturing and automation to drastically reduce the time and skill required to make low-loss, high-strength splices. However, by design these tools were limited to relatively small fibers, typically 250 μm maximum cladding diameter. Before these developments, hand alignment under optical microscopes and flame heat sources were the means used to splice fibers, just as they often are for the large diameter fibers of today's laser applications.
As fiber lasers begin to move from research and development (R&D) to volume production, there is a need to simplify, improve, and automate the steps required for their assembly, as was done for telecom applications. New cleaving and heat source technologies, implemented in a well designed workstation, comprise a substantial step forward in making high power laser manufacturing a high-yield, repeatable process. Flexible capabilities, including multi-axis positioning, wide field optics, and multi-application control software enable splicing, bundling, tapering, cleaving, and end-cap attachment to be performed on the same machine. However, even with such advancements, there remain limitations due to heat sources typically used in optical fiber processing, which increased automation have not resolved.